The Adh gene and its gene product ADH are being used as a system to investigate gene control in Drosophila. Using this system we can utilize chemical selection techniques to isolate Adh-negative mutants. Moreover, the enzyme and its mRNA are present in large amounts and are readily isolatable. We are presently following the following experimental lines: 1. We are determining whether our null mutants possess all or part of the Adh-structural gene. 2. We are determining whether those that do synthesize a messenger RNA of the correct size. 3. We are attempting to develop a procedure that uses immunological methods to detect RNA/DNA hybrids after in situ hybridization.